Depending on where you buy it, your Android phone may be unlocked and can support SIM cards from any carrier, or it could be carrier-locked and require specific SIM cards. While it’s not always clear when an Android device is locked out from accessing other networks, there are ways to check the carrier lock status before you try switching carriers or selling your phone.

The easiest method is to test your phone with a different SIM card:

1. Turn off your phone and remove the SIM card. Recent Android phones require a SIM ejector tool or a paperclip to eject the card.

2. Insert the other SIM card and turn on the phone.

3. Check if you're prompted for an unlock code. Locked phones require a code provided by the service provider.

4. If not, try to make a call. If it connects, your phone doesn’t have a carrier lock, but if you receive any error messages, it's likely that your phone is network locked.

Some devices’ network status can be checked by going to Settings > About Phone to find the network lock header. You can also scan for other network providers by going to Settings > Connections > Mobile Networks, then tapping Network Operators to temporarily disable the auto-selection and manually scan for available networks — if it shows more than one, it’s likely unlocked.

The International Mobile Equipment Identity, or IMEI, is a unique identifier given to every phone that can tell you whether your device is locked. First, go to Settings > About Phone and locate the IMEI header to see the number, which you can then use on a third-party website like imei24.com or to call customer support for a network carrier.

Each option varies in reliability, with switching the SIM card being the most effective way to tell the phone’s carrier lock status. There are several reasons why you should unlock your Android phone, such as dual-SIM models to separate your business and personal numbers without having multiple devices, or to replace your SIM card with an international one when you travel abroad.